I was wonder if there was an OEM swappable replacement master cylinder for a 87 840 that was of larger diameter relative to the OE. I don't like the longer pedal travel and was thinking this would shorten it up nicely, provided such a cylinder exists and is swappable.

The 840 has a unique master cylinder with the outlet pointing up and down rather then off to the side as other models have. It also has a unique bolt pattern where it bolts up to the hydro-boost unit. The 840s also have 4 pot Brembos which require much more fluid for movement then a single pot does.

The bottom line is a longer peddle travel and not much you can do about it unless you go back to single pot calipers that are found on earlier E31 models.

Interesting. Out of curiousity, do late (ie M73) 850s have similar brembo calipers?

Yes, the USA 850M73 has Brembos on the front with the same master cylinder and servo unit as the E31 840.

Interestingly the Euro 850M73 is listed to have a single pot front caliper but still uses the same master cylinder and servo unit.

By the way, the reason they changed the master and servo unit on the 840 is to gain clearance to the head, There is a small offset bracket mounted to the firewall that the servo unit bolts to and as I mentioned the brake line connections to the master cylinder are one on top going up and one on the bottom going down. On The 850M70 both brake lines are attached to the side of the master cylinder and come out straight toward the engine.

The master cylinder one the 840 mounts to the servo unit with 3 bolts as opposed to the earlier E31 <09/93 850M70 that has only two bolts.

Might sound a little weird Ed, But your SS lines shortened my brake travel some, I have Brembo's up front and ///M Calipers in the rear and it now feels and stops great.

Hmm, are the CSi calipers better then (and a swap-in replacement for) the brembo setup? Are the Brembos only in the front?

4 pot Brembos only in the front.

Euro CSI caliper$ and rotor$(I assume that is what you are referring to) are better but only if you replace the entire setup with the Euro CSI rear vented 328X20 rotors and caliper$, otherwise you will upset the brake balance a lot.

USA CSI front calipers are the same as 850M70 calipers, single pot, rears are the same also.

Other then peddle feel, (and of course BLING) bigger brakes will NOT give you any better performance on the street with street tires! If you can get the ABS light on you are at the limit of tire traction and you could triple the amount of clamping force on the rotor and all you will do is get the ABS light on quicker.

4 pot Brembos only in the front.

Euro CSI caliper$ and rotor$(I assume that is what you are referring to) are better but only if you replace the entire setup with the Euro CSI rear vented 328X20 rotors and caliper$, otherwise you will upset the brake balance a lot.

USA CSI front calipers are the same as 850M70 calipers, single pot, rears are the same also.

Other then peddle feel, (and of course BLING) bigger brakes will NOT give you any better performance on the street with street tires! If you can get the ABS light on you are at the limit of tire traction and you could triple the amount of clamping force on the rotor and all you will do is get the ABS light on quicker.

Thanks for the info! I am going to keep the OEM front brembos and try to source a complete euro CSi rear.

Might sound a little weird Ed, But your SS lines shortened my brake travel some, I have Brembo's up front and ///M Calipers in the rear and it now feels and stops great.

Out of curiuosity, where did you source your rear set?

I have gotten many sets in the past directly from friends in Germany, the last set I got at Gault. Calipers aren't bad it is the carrier that is expensive.

Out of curiuosity, where did you source your rear set?You can get them at Gault Bmw, They Cost!!! I originally tried to negotiate them from Brett at KoalaMotorsport, He got a hold of a Euro Csi that was totalled on the right side, I was one of the few all over it, I end up with a few parts from it and negotieated too long on the calipers, He rebuilt them and sold them to a Roadfly member not to far from where i live, He decided after a few months that he didn't wan't to go through the hastle of getting the required rotors, Euro pads etc.... So i jumped all over them!
***I got a Excellent Deal***

Ed! Does this look correct for a 91 850i? I bought it from Germany, It's on the way. Tia!!!

Hartge 19mm

It looks correct. here is a link to all the sway bar stuff for the various models. you will see that the 91,92 have a much more pronounced loop where it goes around the outside of the diff whereas the '93 and later the bar goes behind the diff hanger. I looked for some loose pictures to post but don't have on my website just this PDF.

I think the pictures I have are upside down form yours but it should give you a good comparison. the way your bar picture is it doesn't show the loop well but it looks OK for yours.

Are Hartge bars readily available? 19 mm IMHO is the perfect size for the rear bar. Nothing bigger. Probably should consider to beef up the subframe mounting points for the bar, did they have a kit to do that?

http://www.mwrench.com/Whitepapers/E31antiswaybar.pdf

Scroll down a page to the rear bar section

I bought it as is without mounting hardware, That's the next task! I don't know there sizes, I got lucky and paid under 32Euro for the bar, Shipping is ANOTHER thing$$$

Thanks for the PDF, I've probably been to your sight more than you, Lol!!!

It looks correct. here is a link to all the sway bar stuff for the various models. you will see that the 91,92 have a much more pronounced loop where it goes around the outside of the diff whereas the '93 and later the bar goes behind the diff hanger. I looked for some loose pictures to post but don't have on my website just this PDF.

I think the pictures I have are upside down form yours but it should give you a good comparison. the way your bar picture is it doesn't show the loop well but it looks OK for yours.

Are Hartge bars readily available? 19 mm IMHO is the perfect size for the rear bar. Nothing bigger. Probably should consider to beef up the subframe mounting points for the bar, did they have a kit to do that?

http://www.mwrench.com/Whitepapers/E31antiswaybar.pdf

Scroll down a page to the rear bar section

Interesting! That lists and shows different parts for later 850s and 840s, though both bars are of the same thickness. I am contemplating a CSi front bar addition to my 840 and have already purchased the bar. Are CSi bars compatible with later 840s?

Yes the CSI bar will fit 840 BUT it is REAL close to the bell housing and in some cases it actually touches a bit. Most of the time it touches because the motor mounts have sagged and the engine is lower then normal. I make up a spacer plate out of 1/4 inch aluminum to lower the bar mounts and that is enough for even badly sagging engine mounts.

http://www.mwrench.com/Whitepapers/840spacer.jpg

Unfortunately the CSI bar will not fit the earlier E31s (91, 92)

Are rear bars hard to install? It appears the exhaust has to come down along with the rear subframe...